Wednesday, 22 May 2013

Great Explosion

Lassen Peak is the southernmost active volcano in the Cascade Range with one of the largest lava domes on the Earth.

Great Explosion

On May 22, 1915, Lassen Peak exploded in a powerful eruption that blasted volcanic ash, rock fragments, and pumice high into the air. This created the larger and deeper of the two craters seen near the summit of the volcano today. A huge column of volcanic ash and gas rose more than 10,000 m into the air, and was visible from as far as Eureka, 240 km to the west, on the Pacific Coast.

Pumice falling onto the northeastern slope of Lassen Peak generated a high-speed avalanche of hot ash, pumice, rock fragments, and gas, called a pyroclastic flow, that swept down the side of the volcano, devastating a 8 sq km area. The pyroclastic flow rapidly incorporated and melted snow in its path. The water from the melted snow transformed the flow into a highly fluid lahar that followed the path of the lahar of May 19–20, and it rushed nearly 15 km down Lost Creek to the Old Station. This new lahar released a large volume of water that flooded the lower Hat Creek Valley a second time.

Lassen Peak in snow

The powerful climactic eruption of May 22 also swept away the northeast lobe of the lava flow extruded two days earlier. The eruption produced smaller mudflows on all flanks of Lassen Peak, deposited a layer of volcanic ash and pumice traceable for 40 km to the northeast, and rained fine ash at least as far away as Winnemucca, Nevada, 320 km to the east. Together these events created the Devastated Area which is still sparsely populated by trees due to the low nutrient level and high porosity of the soil.

On August, 1916, Lassen Volcanic National Park was created.